This study identified early behavioral, physical and family characteristics of children with average IQ scores and below average school achievement, approximately 3% of the NCPP population. Low achievers were compared with their IQ-matched academically successful controls on prospectively ascertained indices of cognitive and physical development and family environment. Cognitive deficits and behavioral problems in the preschool period were associated with low achievement at age 7. Socioeconomic status (SES) and family structure were better predictors of low achievement than were indices of physical development or medical status. Low achievers were born into low SES, large families, and two-thirds of them were boys. As preschoolers, they had more language difficulties and lower IQ scores than controls. At age 7, deviant behavior, verbal and non-verbal cognitive deficits, and neurological soft signs were present. Hyperactive low achievers had an increased frequency of obstetrical complications. Sex differences were found in predictors of unexpected academic failure. A summary of major findings has been published in a report on the Collaborative Perinatal Project. This study is completed and a monograph is in preparation.